Aragón Salamanca, A.Alonso Herrero, A.Gallego Maestro, JesúsGarcía Dabó, C. E.Pérez González, Pablo GuillermoZamorano Calvo, JaimeGil De Paz, Armando2023-06-202023-06-2020031-58381-144-3http://cds.cern.ch/record/584999/files/?ln=eshttps://hdl.handle.net/20.500.14352/53497© 2003 Astronomical Society of the Pacific. Conference on Star Formation through Time (2002. Granada, Spain). This research was supported in part by the Spanish Programa Nacional de Astronomía y Astrofísica. AAS acknowledges generous financial support from the Royal Society. AGdP acknowledges financial support from NASA. PGPG acknowledges financial support from the Spanish Ministerio de Educación y Cultura. CEGD acknowledges financial support from the UCM.The [O ii]λ3727 emission line is frequently used as an indicator of the star formation rate (SFR) despite its complex dependence on metallicity and excitation conditions. We have analysed the properties of the [O II] and Hα emission lines for a complete sample of local Hα-selected galaxies, the Universidad Complutense de Madrid (UCM) survey. We find a large scatter in the [O II]/Hα line ratios, although the scatter in the extinction-corrected [O II]^0/Hα^0 ratio is considerably smaller. We also find that the [O II]/Hα ratios are reasonably well correlated with the absolute B- and K-band magnitudes and with EW([O II]). However, the extinction-corrected [O II]^0/Hα^0 ratio is largely independent of these quantities, indicating that extinction is the main driver of the correlations. These correlations allow us to statistically predict-with varying degrees of accuracy-the observed and extinction-corrected Hα fluxes from the observed [O II] flux using the information contained in EW([O II]) and/or the absolute magnitudes, but extreme caution is needed to make sure that the sample selection effects are correctly taken into account.engbook parthttp://cds.cern.ch/open access52Madrid survey galaxiesNearby field galaxiesSpectroscopic propertiesUniversidad ComplutenseO-IIEmissionPhotometryAstrofísicaAstronomía (Física)